Natural gas hydrates are crystalline solids composed of water and gas. In these solids, the gas molecules (guests) are trapped in water cavities (host) that are composed of hydrogen-bonded water molecules. Methane is the main gas in naturally occurring gas hydrates, however carbon dioxide, hydrogen sulfide, and less frequently, other hydrocarbons such as ethane and propane can be found within the hydrate structure. In 1934, Hammerschmidt determined that natural gas hydrates were blocking gas transmission lines, frequently at temperatures above the ice point. This discovery caused a more pragmatic interest in gas hydrates and led to the regulation of the water content in natural gas pipelines.
Gas hydrates can be easily formed during the transportation of oil and gas in pipelines under certain conditions. Factors affecting gas hydrate formation include gas composition, water content, temperature, and pressure, particularly low temperature and high pressure. While these crystalline cage-like structures are initially small, they are able to agglomerate into solid masses called gas hydrate plugs. The formation of gas hydrates within a pipeline often results in lost oil or gas production, damage to transmission lines and equipment, and safety hazard to field workers.
Three types of hydrate inhibitors are currently available to the energy industry for controlling gas hydrates: thermodynamic hydrate inhibitors (THIs), kinetic hydrate inhibitors (KHIs), and anti-agglomerants (AAs). Kinetic hydrate inhibitors are substances that can delay gas hydrate nucleation and crystal growth at a given temperature and pressure. Water-soluble polymers combined with small organic molecules are commonly used as kinetic hydrate inhibitors. The polymers must contain functional group(s) capable of hydrogen bonding to water molecules or gas hydrate particle surfaces and hydrophobic group(s) adjacent to or the hydrogen bonding groups.
Accordingly, there is an ongoing need for compositions and methods that effectively prevent hydrate formations in water and gas transportation and handing processes, particularly those formulations without an oil phase which results in a water cut approaching 100%.